This invention relates generally to a method and apparatus for predicting future coverage of GPS satellites and, more particularly, to a method and apparatus for determining optimal placements of pseudolites as a function of predicted future coverage of GPS satellites.
Global Positioning Satellite (GPS) systems are used extensively in tracking and monitoring the locations of a wide variety of moving objects. For example, open pit mining operations commonly use GPS to track the locations and movements of various earthworking machines, and mobile machines which provide support functions, e.g., servicing, transportation, and the like. In such mining operations, machines such as excavators, wheel loaders, track-type tractors, and the like, perform earthworking tasks such as digging, loading, leveling, and such. Other machines, such as off-road mining trucks, perform other tasks such as hauling. The complex interactions of these machines has resulted in a great need to track and monitor their activities, and GPS has become increasingly depended upon to perform this monitoring.
It is widely known that GPS involves the use of a number of satellites which orbit the earth in known, non-geosynchronous orbits. For example, the system used by the United States, i.e., NAVSTAR, uses twenty-four (24) satellites, which are spaced apart in various orbits. For many applications, at least three (3), and preferably at least four (4), satellites are in line-of-sight view by a GPS antenna and receiver located on the surface of the planet, thus providing the GPS receiver with the needed data for position determination.
However, situations exist in which some GPS satellites are obscured from view, thus not allowing the minimum number of satellites to be used. In these situations, GPS systems cannot function as desired, and position determination may not be possible. For example, in the open pit mining operation noted above, the rugged terrain, e.g., cliff faces, deep pit areas, and the like, may obscure satellites from view and prevent GPS from being used effectively.
A technique which has been developed to counter the above situation is to place false GPS satellites, known as pseudolites, at strategic earth-bound locations to compensate for the lack of true GPS satellite information. These pseudolites function in the same manner as true GPS satellites, providing a signal similar to GPS signals to further enable position determination. Typically, the pseudolites are placed in areas in which problems with GPS coverage have been known to occur, and thus are used to overcome a situation which has already been determined to exist.
Currently, there are no known means disclosed in the art which take advantage of the ability to predict the future location of GPS satellites to determine future GPS coverage over an area at a site based on terrain data, and subsequently provide a means to compensate for inadequacies in GPS coverage prior to problems actually occurring.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method for determining a desired position of a pseudolite at a site is disclosed. The method includes the steps of predicting an area of coverage of the site by at least one GPS satellite, determining a condition of reduced coverage as a function of the predicted area of coverage, displaying the area having reduced coverage on a terrain map, and placing a pseudolite at a location at the site to provide coverage in the area having reduced coverage.
In another aspect of the present invention a method for determining a desired position of a pseudolite at a site is disclosed. The method includes the steps of predicting an area of coverage of the site by a plurality of GPS satellites, determining a condition of reduced coverage as a function of the predicted area of coverage, displaying the area having reduced coverage on a terrain map, placing a pseudolite model on the terrain map at a desired location, displaying an area of coverage of the pseudolite model on the terrain map, and displaying a change in coverage of the area having reduced coverage as a function of the area of coverage of the pseudolite model.
In yet another aspect of the present invention a computer-based method for determining a desired position of a pseudolite at a site is disclosed. The method includes the steps of predicting areas of coverage of the site by a plurality of GPS satellites, determining a condition of at least one area at the site having reduced coverage as a function of the predicted areas of coverage, displaying the areas on a terrain map, the displayed areas indicating a level of coverage, determining an optimal location of at least one pseudolite model as a function of reduced coverage of the at least one area, displaying the at least one pseudolite model at the optimal location on the terrain map, and updating the terrain map display to indicate revised coverage in the areas as a function of the coverage of the GPS satellites and the at least one pseudolite model.
In yet another aspect of the present invention an apparatus for determining a desired position of a pseudolite at a site is disclosed. The apparatus includes at least one mobile machine located at the site, a GPS receiver located on the mobile machine for receiving signals from a plurality of GPS satellites, a display for indicating a terrain map of the site, and a processor. The processor is adapted to predict a future area of coverage of the site by the plurality of GPS satellites, determine a condition of predicted reduced coverage in at least one area of the site, and provide information to the display to indicate the at least one area having reduced coverage, the area having reduced coverage being indicative of a desired position of a pseudolite at the site.